1. Field of the Invention
The present invention relates to a technique of a magnetic head of a magnetic recording disk device such as a magnetic disk drive and a magnetic tape drive and its magnetoresistive sensing element, and more particularly to a giant magnetoresistive sensing element (hereinafter referred to as "GMR") and a magnetic head and a magnetic disk device using the GMR.
2. Description of the Related Art
As a magnetic recording density has been made higher, a head higher in a signal magnetic field sensitivity has been required. An initial magnetic induction thin-film head cannot be adapted to the recording density of more than 1 Gbit/inch.sup.2. Instead of this type, there has been developed a magnetoresistive head using the magnetoresistance of a ferromagnetic metal thin film as a head high in read sensitivity. However, it has been found that this magnetoresistive head similarly has lacked for the read sensitivity in reading the magnetic recording in a high-recording density region of more than 3 Gb/inch.sup.2, and therefore it has been expected to realize a high-sensitive magnetic head superior to the magnetoresistive head.
Under that circumstances, a magnetic head using a magnetic element with a spin valve structure has been proposed in 1994, and several experimental studies have been made.
The outline of the structures of those magnetic heads will be described below.
In a slider-shaped magnetic head shown in FIG. 1, a head element 2 that detects a magnetic field includes a giant magnetoresistive sensing element (magnetic field sensor) 18 shown in FIG. 2, and an inductive recording element (not shown) comprised of a plurally-wound coil pattern 7 and a soft magnetic yoke (not shown) surrounding the coil pattern 7. In FIG. 1, denotation 4 means electrode terminal and denotation 5 means signal wise magnetic field represented by Hy and denotation 6 means track widthwise magnetic field. In FIG. 2, denotation 17 means fixed magnetization and denotation 19 means medium magnetization.
In the case where the magnetic head thus structured is located on a recording medium 20 shown in FIG. 2, that is, a magnetic disk, to obtain a read output, a signal magnetic field 5 perpendicular to an air bearing surface 3 (hereinafter referred to as "ABS 3") shown in FIG. 1 is detected. The principle of the detection of the signal magnetic field is shown in FIG. 2.
In general, the giant magnetoresistive sensing element 18 is of the structure in which a magnetic fixed layer 11 and a magnetic free layer 13 are opposed to each other through a conductor layer (not shown) of 2 to 3 nm in thickness as shown in FIG. 2. The signal magnetic field from the recording medium 20 makes a direction of magnetization of the magnetic free layer 13 vibratingly rotate. In this situation, assuming that an angle defined between the magnetization M of the magnetic free layer 13 and the fixed magnetization 17 of the magnetic fixed layer 11 is .theta., a resistance change .delta.R is represented by .delta.R=-(1/2).DELTA.R.multidot.cos .theta., where .DELTA.R represents a maximum resistance change (refer to FIG. 3).
As usual, the degree of a response of the resistance change .delta.R to the signal magnetic field represents the magnetic field response sensitivity of the giant magnetoresistive sensing element. Even in the case where it is judged whether an element is good or bad in quality as the magnetic head during an inspection process, a magnetic field in the signal direction is applied from the exterior to evaluate the .delta.R of that element. Because the sensitivity to a magnetic field in a track widthwise direction perpendicular to the signal magnetic field is irrelevant to the operation of the element up to now, it has not been disclosed in the above prior art at all.
A conceptual diagram of those conventional giant magnetoresistive sensing element structures is shown in FIG. 9.
In those conventional examples, a magnetic easy axis 27 (uni-axial anisotropy) of the magnetic free layer 13 having the sensitivity in the signal magnetic field 5 is disposed perpendicularly to the signal magnetic field 5 so that the magnetic free layer 13 is liable to be subjected to domain stabilization with a single domain structure, and in addition, in order to ensure the domain stabilization with the single domain structure, a longitudinal bias magnetic field Ht 28 is applied to a direction (track widthwise direction 41) perpendicular to the signal magnetic field 5 by a permanent magnet film.
As a result, as shown in FIG. 10, no hysteresis occurs in a response curve of the resistance change .delta.R of the spin valve element to the magnetic field in the signal magnetic field direction.
However, the magnetic field response sensitivity (MR sensitivity) in the above conventional example is less than 1, as shown in FIG. 11, according to the simulation result using a so-called coherent magnetization rotation model. In the present specification, MR sensitivity=1 means a case in which the resistance change .delta.R when the signal magnetic field intensity Hy equal to Hk is applied is equal to 1/2 of the maximum resistance change .DELTA.R. There has been found from the results of the inventor's study that there arises the following problem. That is, as the longitudinal bias magnetic field Ht is applied, the MR sensitivity reduces monotonously with the result that the sensitivity is deteriorated to 1/2 or less by the longitudinal bias magnetic field of only Ht=Hk (Hk is uni-axial anisotropy). Also, it has been proved from the inventor's study that there arises such a problem that in the case where the magnetic free layer 13 is arranged in a direction of the magnetic easy axis 27 as shown in FIG. 9, the magnetic response sensitivity of the resistance change .delta.R in the signal magnetic field direction becomes lower than the sensitivity of the magnetic field response perpendicular to the signal magnetic field direction.
The prior art gives rise to such a problem that the sensitivity is deteriorated by the provision of means for permitting stable operation in the spin valve head which is designed so as to obtain the high sensitivity.